In general, in order to manufacture a semiconductor integrated circuit or the like, a target object such as a semiconductor wafer or the like is repeatedly subjected to various processes such as a film forming process, an etching process, an oxidation/diffusion process, a reduction process and the like. Recently, various metal films such as Ta, Ti, Cu and the like are formed by the film forming process. In order to form such metal films, there is widely used a liquid source material having a low vapor pressure and a liquid state at room temperature and one atmospheric pressure. The liquid source material is force-fed to a vaporizer and then is vaporized therein by being heated in a depressurized atmosphere, thus becoming a source gas. The source gas is supplied together with a carrier gas into a depressurized processing chamber. Then, a metal thin film is deposited on a semiconductor wafer accommodated in the processing chamber by CVD (chemical vapor deposition).
An example of the vaporizer is disclosed in JP2001-148347A. In this vaporizer, a force-fed liquid source material at a controlled flow rate is introduced via a valve port into a heated vaporization chamber set in a depressurized atmosphere and then is vaporized therein, the valve port being opened and closed by a valve body. Simultaneously, a carrier gas is supplied into the vaporization chamber, thereby facilitating atomization of the liquid source material to increase a total surface area thereof. As a result, vaporization of the liquid source material is facilitated, enabling efficient generation of the source gas.
In the above-described vaporizer, the liquid source material should not remain in a downstream space of the valve port when the vaporization is stopped. However, when the carrier gas is supplied into the vaporization chamber as described above, there exists a small amount of so called dead space, i.e., an area where the carrier gas does not reach sufficiently. The liquid source material coming into the dead space is not vaporized readily so that it may remain unvaporized in the vaporization chamber even after finishing the operation of the vaporizer. In case the liquid source material is an organic metal complex having low thermal stability, the liquid source material remaining in the vaporization chamber is thermally decomposed therein to become deposits.
If fragments of the deposits are discharged from the vaporization chamber, they clog downstream passages and then are introduced as particles into the processing chamber. As a result, a production yield and reproducibility of the CVD process deteriorate.